Experience-dependent development of dendritic arbors in mouse visual cortex

Abstract

17 65 processes. For the first time, we also establish Rem2 -a small GTPase previously implicated in 66 dendritic complexity in vitro and in Xenopus Laevis optic tectum [51, 53-55] -as an experience-67 dependent negative regulator of dendritic complexity in mammalian visual cortex. This work 68 demonstrates that Rem2 cell-autonomously regulates the arrangement of the basal dendrites: 69 neurons in which Rem2 has been deleted are less likely to exhibit a significant directionality and 70 sometimes exhibit abnormal directionality. Taken together, our results establish a unified 71 framework for investigating dendritic development in the mammalian cortex and expand our 72 understanding of how dendritic arbors are established and maintained in an experience-rich 73 environment. 74 75 Methods 76 Golgi-Cox Labeling and Tissue Preparation 77 Typically-reared WT and Rem2 -/littermate mice were housed in a 12hr light/12hr dark 78 cycle from birth until the specified age (P7, P12, P16, P21, P30). Dark-reared mice were placed 79 in a light-tight box beginning at P9 until termination of the experiment (P16, P21, or P30). At 80 the specified age, mice were anesthetized with ketamine/xylazine cocktail (ketamine 81 100mg/kg, xylazine 10mg/kg) and transcardially perfused with 0.9% saline in ddH20. Dark-82 reared mice were anesthetized in the dark and then shielded from light until after perfusion 83 using a mask constructed of several layers of light blocking tape (Thor Labs) to cover the eyes. 84 Immediately following perfusion, brains were weighed and submerged in Golgi-Cox solution (FD 85 NeuroTechnologies). Throughout all steps involving Golgi-Cox, brains were protected from light. 86 Golgi-Cox solution was changed 24 hours after initial immersion and brains continued to be 87 stored in Golgi-Cox solution for 7 days. After 7 days, brains were transferred to Solution C (FD 88 NeuroTechnologies) for at least 2 days. Coronal sections were cut at 150 µm using a cryostat 89 and immediately mounted on slides coated with 2% porcine gelatin. Histology was carried out 90 according to the protocol supplied by FD NeuroTechnologies RapidGolgi Stain Kit. Briefly, slides 91 were washed with ddH2O, developed using FD Neurotechnologies Solutions D & E, rinsed in 92 ddH2O, dehydrated with a graded series of ethanols, and cleared using xylenes. Slides were 93 then coverslipped using Permount (Fisher Scientific).94 95 TdTomato Reporter Tissue Preparation 96 Typically reared Rem2 +/+ ;TdT flex/flex and Rem2 flx/flx ;TdT flex/flex mice were housed in 12hr 97 light/ 12hr dark cycle from birth until the specified ages and days post injection (dpi) (5dpi/P25, 98 7dpi/P27, 10dpi/P30). Mice (both Rem2 +/+ ; TdT flex/flex and Rem2 flx/flx ; TdT flex/flex ) were injected 99 with AAV.GFP-Cre at P20 (see detailed method below) to activate reporter expression and, in 100 Rem2 flx/flx ; TdT flex/flex mice, manipulate Rem2 expression. At the specified age, mice were 101 anesthetized with ketamine/xylazine cocktail (ketamine 100mg/kg, xylazine 10mg/kg) and 1...

Tau and α-synuclein shape microtubule organization and microtubule-dependent transport in neuronal dendrites

“…This also applies to the maturation of the dendritic processes because the dendritic architecture fundamentally determines the functional capacity of neurons. During early postnatal development significant dendritic process formation takes place in various brain areas (Kolb and Fantie, 1997) (Richards et al, 2020) and the formation and pruning of dendritic processes determine the density of the neural network in which individual neurons become embedded. Given the unique function and shape of the dendritic arbor, the integrity of the microtubule cytoskeleton and proper transport processes are crucial during dendritic process formation (Bramham and Wells, 2007; Penazzi et al, 2016).…”

“…This also applies to the maturation of the dendritic processes because the dendritic architecture fundamentally determines the functional capacity of neurons. During early postnatal development significant dendritic process formation takes place in various brain areas (Kolb and Fantie, 1997) (Richards et al, 2020) and the formation and pruning of dendritic processes determine the density of the neural network in which individual neurons become embedded.…”

Dysregulation of astrocyte-secreted pleiotrophin contributes to neuronal structural and functional deficits in Down Syndrome

“…In the visual cortex (VC) dendrite outgrowth is prominent from birth 22 , synapse formation is high from P7 23,24 , synaptic maturation begins ~P14 25 and circuit stabilization is achieved by ~P120 (Figure 1A). In neurotypical development Ptn has widespread expression throughout the brain, and prominent expression in upper cortical layers (Figure S1A-A').…”

“…To ask how Ptn expression correlates with important periods of synaptic development, we utilized a previously published astrocyte RiboTag RNA-sequencing dataset of the visual cortex 16 to determine the temporal profile of Ptn expression. In the visual cortex dendrite outgrowth is prominent from birth 17 , synapse formation is high from P7 18,19 , synaptic maturation begins ~P14 20 and circuit stabilization is achieved by ~P120 (Figure 1A). We found that peak Ptn expression correlates with periods of synaptogenesis and synaptic maturation (Figure 1B).…”

Dendritic branch structure compartmentalizes voltage-dependent calcium influx in cortical layer 2/3 pyramidal cells

“…Our experiments were conducted in juvenile mice (between P21-P28). Although the dendritic branch structure is static after this age (Koleske, 2013, Richards et al, 2020, it is possible that changes in channel composition dampen the effects of dendritic branch structure on excitability. We show that such effects are possible with compartment models (Figure 7F), and it is known that changes in dendritic excitability can occur as a result of synaptic plasticity induction (Frick et al, 2003, Frick et al, 2004, Losonczy et al, 2008.…”